Diamond HK36 N40440 accident near Bend, Oregon

Probable cause

An condition, which could not be determined because postaccident examination of the airframe and engine did not reveal any anomalies that would have precluded normal operation, that prompted the pilot to discontinue the flight. Contributing to the accident was the pilot's decision to attempt to return to the runway instead of landing straight ahead in the field off the runway end.

NTSB analysis

Two witnesses observed the motorglider depart from runway 16, appear to have difficulty climbing, and then make a left circling turn in an apparent attempt to return for a landing. The airplane struck an unoccupied factory on the southeast corner of the airport. Damage signatures indicated that the right wing struck the building about 8 feet above the ground while the airplane was in an approximate 30-degree right bank. Ground scars and propeller damage indicated that the engine was running at the time of impact. The pilot had owned the airplane about 9 years, but his experience in the airplane could not be determined. The pilot's autopsy and toxicology results did not reveal any conditions that would have affected the pilot’s operation of the motorglider. Examination of the flight control system and the engine did not reveal any preaccident mechanical conditions or failures that would have precluded normal operation or warranted an immediate turn back for landing. The propeller blade pitch and most cockpit controls were found in their normal or expected positions/settings.

However, several conditions that could have contributed to or been indicative of operational difficulties were observed. The circuit breaker for the propeller pitch control was found in the "out" (circuit disabled) position; testing indicated that the breaker was functional, and complied with the manufacturer's specifications. It could not be determined when or how the breaker came to be set to that position. The airplane pitch trim control was found in the full airplane nose-up position instead of the neutral position, but the reasons for this could not be determined. Throughout its range, the tachometer indicated about 15 percent lower than the actual propeller rpm. The nest of a paper wasp, which was likely occupied by a few insects during the attempted flight, was found in the cockpit air inlet, and it is conceivable that the wasps were disturbed and entered the cockpit after takeoff. Since the canopy could not be opened in flight, the presence of the wasps could have prompted the pilot's turn back.

Neither the actual climb rate nor the maximum altitude of the airplane could be determined. Therefore, it could not be determined whether the pilot's decision to return for landing was based on the airplane performance, one of the discrepancies noted above, or some combination thereof. Examination of the cockpit indicated that only the takeoff checklist was readily available to the pilot at the time of the accident and that the emergency and other procedures checklists remained inside the flight manual, which was stowed in an undetermined location for the flight. Although an emergency landing on the terrain south of the airport and more closely aligned with the departure heading probably would have damaged the airplane, it also would have likely resulted in a more successful outcome.

Text from the NTSB. Open the NTSB docket for WPR10FA388 for the full record.